Method of operating film evaporators



March 18, 1952 c. F. ROSENBLAD 2,589,733

METHOD OF OPERATING FILM EVAPORATORS Filed Sept. 11, 1946 STEAM FROM I f VAPOR FROM OUTSIDE SOURCE I6 LIQUID L0, {VA' If, 2 I I I I '"Z 5 4 ,,1I g 4,, I 33) $221 a i1 3* I if HEATING MEDIUM i I I I 9 I5 5 I 4 2 s 1 j I I 5 5 3 5 I I 5 4 i l I 6 5 U I i a I I I I i; I 8 5 I 9 g I I I g CONDENSATE (ac LIQUID TO BE l2 EVAPORATED u 7 I I I INVENTOR. E CURT FREDRIK ROSENBLAD AT TORNEY Patented I Mar. 18,1952

2,589,733 METHOD OF OPERATING FILM EVAPORATORS Curt Fredrik Rosenblad, Stockholm, Sweden, as-

signor, by mesne assignments, to Rosenblad Corporation, New York, N. Y., a corporation of New York Application September 11, 1946, Serial No. 696,366 In Sweden July 5, 1943 Section 1, Public Law 690, August 8, 1946 Patent expires July 5, 1963 1 Claim. (Cl. 1832.5)

The present invention relates to methods of operating film evaporators or such type of apparatus in which the liquid to be evaporated is distributed over the heating surface which may consist of substantially vertical tubes or parallel plate walls, for instance, so as to form a relatively thin liquid film upon the surface flowing downwardly along the same.

In operating this type of apparatus it happens particularly often with many liquids that severe trouble is caused by a tendency of the liquid to be transformed into foam, mostly when starting operation. This has been found to be due to the presence. of air or gas in the space through which the liquid is passed and in consequence thereof it is obvious that the danger of foaming must be greatest at the start, since at that time the whole space is normally filled with air. But, of course, even such quantities of air or gas which may be dissolvedor otherwise carried with the liquid and liberated upon the heating thereof may cause foaming during operation. It is also natural that trouble with foaming will occur more often in film evaporators than in other types of apparatus because in film evaporators the free liquid surface is relatively large as is also the space available for liberated steam and gas.

With this in view it is an object of the invention to establish such operating conditions as to eliminate or at least substantially diminish the danger of foam forming in apparatus of the kind described.

Thus, one object of the invention is to introduce steam from an outside source into the space at the surface to be passed by the liquid in connection with starting operation in order to rapidly drive out any air or gas, contained in such space.

Another object of the invention is to de-gas the liquid before it is supplied to the evaporator, as by indirectly heating the liquid or subjecting the same to vacuum under suitable conditions so that no material quantities of gas or air will be liberated from the liquid in the evaporator.

Further objects of the invention will be evident from the following.

Thus, the invention contemplates that in connection with starting operation by supplying the liquid and a heating medium to different spaces at opposite sides of the heat exchange surface in the evaporator to be passed therethrough in heat exchange relation, steam is forced from an outside, source through the space at the liquid side during some period when admitting the first liquid to the evaporator. This temporary steam flow through the evaporatoring space will carry V 2 with it any gas or air contained therein before starting and drive out such objectionable fluids which may escape through the ordinary discharge means.

5 v As may be desired according to circumstances thegas-removing steam flow may be commenced and finished shortly before admitting the liquid to the evaporator or possibly simultaneously therewith and even immediately after the feed of liquid has begun, all of which may be said to jbe concomitant with the initiation of the heat {exchange process. a

In some cases this measure may be sufficient to eliminate foaming butin'other cases when the liquid may liberate unduly great quantities of air 11; or gas at the evaporating temperature, it may in addition be necessary to de-gas the liquid before it is supplied to the evaporating space in the evaporator. I

This may be effected outside the evaporator in ,any conventional device known to the artfor such purpose or possibly by corresponding arangements in a compartment of the evaporator,

either as by heating the liquid indirectly to a suitably high temperature or, for instance, by subjecting the liquid to vacuum.

Thus in the case of application of vacuum to the liquid this may conveniently be carried out in a separate vessel with an outlet for gas connected to the condensor or its air pump with which most evaporation plants are provided.

, Of course de-gassing of the liquid may also be eifected by simultaneous heating and subjection 1 to vacuum in case this is preferred.

De-gassing of the liquid may be restricted to a suitable period after starting operation or continually performed the whole working time or as otherwise may be desired.

With multiple stage evaporating plants de- 40 gassing of the liquid is of course needed, if at all, only before entering the first stage, whereas eliminating of gas content from the evaporating space of the different evaporating units should be performed with all of them.

As regards evaporators with forced pump circulation of the liquid through a return conduit in particular, it is generally rather important N that the liquid feed is degassed at least during the first stage of operation before the circulation pump is started so that the circulating liquid 1, will carry no substantial quantities of gas, be-

cause otherwise the pump action may facilitate liberation of such gas and cause foaming.

The employment of the method according to 5 the invention thus in many cases totally eliminates any danger of foaming in the evaporator or in other casesatleast reduces the foam trouble to rather ;negligible proportions with the material advantage that as a rule it is thereby rendered possible to eliminate any such large and costly devices for separation of foam from the main liquid body which are otherwise indespensible in the handling of many liquids; and

should further measures eventually be required to control the liquid flow it will then nearly always be sufficient to use foamv extinguishing chemicals.

The invention may be carried into effect by any suitable form of conventional apparatus, and

by way of example but without limitation the ac-- Letters Patent is:-

companying drawing shows schematically one form of apparatus suitable for the purpose. In the drawing a vertical film type evaporator I is provided with upper chamber 2 and a--lower chamber 3 connected by means of a tube 4 spaced from' the' outer-wall of the evaporator and extending'upwardly into the chamber 2. The bottom chamber 3 is connected by means of pipes 5 and 5 and pump I with the chamber 2, this structure forming a closed system for circulating liquid to be evaporated in tube 4, into which it overflows fromv chamber 2 to pass in the form of a film downwardly over the interior surface of the tube. Between the tube 4 and the outer shell there is formed a heating chamber 8 to which heating: steam is admitted .through the valved inlet 9 and from which the condensate is removed through the valved outlet 10. Liquid to be evaporated is supplied through the valved connection l2, the vapor therefrom'being discharged through the valved outlet H. Suitable valved drains are provide'dsuch' as those indicated at 7 l3, l4 and 15. Steam from anoutside source for driving gaseous fluid from the liquid side of the apparatusis admitted through the-valved con- The method of operating film evaporators comprising the'steps of supplying liquid to be evaporated and a heating medium to separate spaces at opposite sides of the heating surface in the evaporator to be passed through the same in heat exchange relation, and concomitantly with the initiation of such heat exchange process forcing steam from an outside source through the space at the liquid side of the heating surface to drive out any gaseous fluid which may b contained in the last mentioned space.

' CURT' FREDBIK ROSENBLAD.

REFERENCES CITED The following references are of record in th file of this patent:

UNITED STATES PATENTS Number Name Date 377,099 Fowler Jan. 31, 1888 806,696 Moody Dec..5,"1905 1,006,197 Frasch Oct. 17, 1911 1,013,091 Kestner Dec. 26, 1911 1,072,670 Strite Sept. 9, 1913 1,778,079 Kristensson Oct. 14, 1930 2,088,213 Perkins July 27,1937 2,291,228 Jenson July 28, 1942 2,374,232 Pfeiffer-et al. Apr. 24, 1945 la-Alena, 

